Digital dermatitis (DD) is an economically important polymicrobial disease process of dairy cattle that, remains etiologically undefined. It is the leading cause of lameness in dairy cattle in the United States of America. In addition to the cost associated with treatment and lost production, DD represents a significant welfare concern for the industry.
In countries where DD is widespread, footbaths containing antibiotics are often used. These footbaths rapidly become contaminated with feces and dirt and hence function as large selective cultures of antibiotic resistant bacteria. In Sweden tetracyclines are used, but only for topical treatment of individual animals since on herd level footbaths with copper sulphate are recommended.
To date no commercial vaccine or serologic test for DD is available. Although the disease is responsive to antibiotics, a definitive bacterial cause has not been identified. Many bacteria of different genera, such as Treponema, Fusobacterium, Dichelobacter, Prevotella, and Porphyromonas have been isolated from DD lesions. Treponema spp. are regularly isolated from DD lesions, however attempts to induce classic disease lesions with pure culture of these microorganisms remain universally unsuccessful.
Several phylotypes of Treponema can be present in the same lesion. Different phylotypes have been isolated from the same animal and by cloning and sequencing of 16S rRNA genes, five different phylotypes were identified in a pooled sample from four cows. It has also been demonstrated by fluorescence in situ hybridization on biopsies from DD lesions that the distribution in the dermal layers differs between phylotypes.
In addition to the numerous phylotypes of Treponema within even a single lesion, and the lack of efficacy of Treponema based vaccines, it is widely believed that the disease is polybacterial in nature. The identity of microorganisms that work in concert with Treponema spp. to cause the clinical presentation of DD in cattle has remained unknown. Lack of this knowledge is an important problem because it prevents the development of effective intervention strategies that target the causative agents of DD. One important tool for studying this disease process is the development of a consistent model of disease induction that results in lesions characteristic of the naturally occurring lesions. Such a model will allow for in-depth study of the disease pathogenesis, experimental studies to try and fulfill identification of causative organisms and most importantly a model useful for testing experimental interventions. Identity of the causative organisms allows for the development of vaccines, treatments, and preventative agents.
As can be seen a need exists in the art for animal models, identification of causative agents and development of vaccines, treatments and preventative agents.